Conventional DIN cables.

Connect the soundcard's 'MIDI out' to the first synth's 'MIDI in', take a 'MIDI Thru' out from that and connect it to the next machine's 'MIDI in', take a 'MIDI Thru' out from that and connect it to the next machine's 'MIDI in', and so on.

You'll need to tell each synth/module which midi channel it should use It's normally pretty simple, but you'll have to read the blurb to find out how for the equipment that you intend to use.

Ed